(1) Field of the Invention
This invention relates to a fuel pump used for an automobile or the like, and more specifically to an improvement of a fuel pump driven by an electric motor, supplying fuel to an injector at a high pressure, and constituting a part of means for injecting fuel to an engine in response to signals from an electronic control device.
(2) Description of the Prior Art
A displacement pump has been hitherto mainly used for feeding fuel with a high pressure, a discharge pressure of the pump being about 2 or 3 kg/cm.sup.2. The displacement pump, however, has disadvantages that high accuracy of working is required for obtaining a desired performance, thus resulting in a high cost, and the discharge pressure greatly pulsates due to the displacement type, thus resulting in high vibration and noise.
It has been known for solving the aforesaid disadvantages to use a regenerative pump as a fuel pump. The regenerative pump used as the fuel pump is described in, for example, U.S. patent application Ser. Nos. 362,855 filed on Mar. 29, 1982, now U.S. Pat. No. 4,451,213; 366,688 on Apr. 8, 1982, now abandoned; 377,546 on May 12, 1982; 369,426 on Apr. 19, 1982; 370,350 on Apr. 21, 1982, now U.S. Pat. No. 4,478,550; 372,169 on Apr. 26, 1982, now U.S. Pat. No. 4,445,821; 372,377 on Apr. 27, 1982, now U.S. Pat. No. 4,403,910; 378,724 on May 17, 1982; 405,579 on Aug. 5, 1982; 445,222 on Nov. 29, 1982 and 505,849 on June 20, 1983.
When an automobile runs under a severe load condition such as running on a sloping road in high ground and in a high temperature, a fuel temperature in a fuel tank rises gradually, thus often resulting in occurrence of bubbles of fuel vapor in the fuel tank. Then, the fuel pump sucks not only fuel but also the bubbles through a suction port, or sucks only the fuel vapor in an extreme state, so that a rise in fuel pressure is not performed in the fuel pump. As a result, a vapor-lock phenomenon occurs and an engine stops.
It has been known to provide the regenerative pump with a vapor vent midway of a pump passage in order to discharge the above-mentioned fuel vapor out of the fuel pump. The regenerative pump of this type can discharge vapor in a pump chamber during a starting operation of the pump, and further discharge vapor caused by cavitation during a normal operation of the pump. The conventional vapor vent, however, only connects the pump passage with the outside of the pump, thus it is inevitable that not a small amount of the fuel is discharged to the outside of the pump through the vapor vent even in case of including no fuel vapor. The fuel pump provided with the vapor vent is disclosed in, for example, U.S. Pat. No. 3,418,991.